1. Field of the Invention
This invention relates to truck brake systems having primary and secondary circuits where provision is made for controlling a spring brake through a foot pedal in the absence of primary circuit function. More particularly, the application is directed to integrating a quick release valve into a spring brake valve.
2. Discussion of the Art
Presently available truck brake systems include primary and secondary pneumatic circuits for selective application of the vehicle brakes. Brake chambers are associated with a first or front steering axle and, likewise, brake chambers are provided for a second or rear drive axle. The brakes are applied by selectively depressing a foot pedal to actuate a control valve and deliver pressurized air from a primary or secondary reservoir to the brake chambers associated with the axles. The primary circuit supplies pneumatic pressure to the rear or drive axle brakes and the secondary circuit supplies air pressure to the front or steer axle brakes.
If the primary circuit fails, the secondary circuit is still available and is mechanically opened via a push-through force from the driver's foot to assure braking function to the steer axle. Spring brakes, which are large mechanically applied springs associated with the drive axle used to park the vehicle, are usually held in a release position by supplying air pressure to a spring brake chamber associated with the rear brakes. This allows the vehicle to roll. When air is exhausted from the spring brake chamber, the mechanical spring brake is actuated and performs the braking function. Thus, by selectively connecting the brake actuator to an exhaust port or atmosphere, the mechanical spring brake is selectively applied. In addition, if the primary circuit fails, the spring brake is applied and modulation of the braking function is provided through the foot control valve.
These known arrangements use a separate spring brake quick release valve. The quick release valve improves the response and allows air to exhaust from the spring brake chamber quickly. The quick release valve also maintains sensitivity of foot control in those situations where the primary circuit has failed. U.S. Pat. No. 4,596,265, commonly owned by the assignee of the present application, illustrates a known quick release valve used in a pneumatic pressure braking system. Separate lines lead from the quick release valve to the spring brake chambers and, in addition, a line interconnects the spring brake valve with the spring brake quick release valve. This arrangement requires a number of individual components such as the quick release valve housing, associated pneumatic lines, fittings or connectors, etc., and there are also attendant service issues related thereto. Moreover, customers find the present system overly complex and expensive to install.